The present invention relates to electronic devices, and more particularly to a pressure test wafer capable of measuring the pressure at several points on the pressure test wafer inside a chamber while gas is flowing into and/or out of the chamber.
Chambers are used in many types of processing systems. Examples of such processes include chemical vapor deposition (CVD) processes, such as plasma-enhanced CVD (PECVD) processes, and dry etch processes, among others. Typically, a substrate, such as a semiconductor wafer, is placed in the vacuum chamber and conditions in the chamber are set and maintained to process the substrate in a desired fashion. Generally, it is desirable to minimize the processing differences, such as the thickness of a deposited layer or the depth of an etch, across the wafer.
Minimizing the process differences across a wafer depends on controlling the parameters that affect the process, such as wafer surface temperature, gas flow rates, and chamber pressure. Variations in processing parameters across the wafer can result in nonuniform processing.
Often, variations in a processing parameter are inferred by evaluating trial wafers that have been processed under various conditions rather than by measuring the parameter directly. For example, the thickness of a CVD layer may be measured at several points across each wafer in a series of wafers processed at different nominal chamber pressures to evaluate the effect of pressure on the thickness of the layer. The nominal chamber pressure is typically measured by a pressure gauge at a single point of the chamber. However, the nominal chamber pressure does not necessarily indicate either the actual pressure at the surface of the wafer or the local pressure ;variations that can occur across the surface of a wafer arising from the dynamic effects of the gas flow.
Additionally, conventional methods for evaluating process parameters by using a series of trial waters can be time-consuming, expensive, inaccurate, and provide limited data. The methods are time-consuming because typically several wafers must first be processed, and subsequently evaluated. The methods are expensive because they consume both trial wafers and the cost of repeated process runs that could otherwise be devoted to production. The methods are inaccurate and provide limited data because the measurement is a secondary measurement (e.g., of film thickness) rather than at direct measurement, of the local pressure for example, and because the observed change may not have been caused by a variation in the test parameter.
Therefore, it is desirable to provide a device and a method for directly measuring the pressures at and across the surface of a wafer in a processing chamber under dynamic gas flow conditions.
The present invention provides a device and a method for measuring the pressure across the surface of a test wafer during simulated processing conditions. The simulated process may be, for example, a CVD process or an etch process. In an exemplary embodiment, la plurality of micro-electro-mechanical systems (MEMS) pressure sensors are arranged across the surface of a test wafer. The pressure sensors are attached to wires that lead outside of a processing chamber. Electrical signals from the pressure sensors are measured under simulated wafer processing conditions to determine the pressure at the various pressure sensors. Processing parameters, such as nominal chamber pressure, gas flow rates, exhaust rates, and wafer position may be varied to determine the effect these parameters have on the pressure present at the surface of the wafer.
In another embodiment, the MEMS pressure sensors are fabricated in a test substrate, and conductive interconnects bring the electrical signals from the pressure sensors to the edge of the substrate. In a further embodiment, the MEMS and the interconnects are fabricated to withstand higher processing temperatures and incorporate high-temperature metallization layers. In another embodiment, the MEMS pressure sensors are optimized to provide greater sensitivity within an expected pressure range.
These and other embodiments of the present invention, as well as some of its advantages and features, are described in more detail in conjunction with the text below and attached figures.